[craig mcarthur] "I record gameplay using my Haupaugge HD PVR in an mp4 format,"
You should be recording these as AVCHD files. They will edit easier in Vegas. I'm guessing you slelected the XBOX option because you are recording from an XBOX but actually, that option is for PLAYING on an XBOX which you are not doing (because you are editing in Vegas which is running on a PC). So you should be recording as AVCHD.
[craig mcarthur] " whenever I import these to Vegas its as if the video is 'too big' for the preview box as it only displays the top left corner of the video. "
Right-click on the preview window and select
Scale Video to Fit Preview Window. See if that fixes it.
~jr
http://www.johnrofrano.com
http://www.vasst.com 
